1. Field of the Invention
The present invention relates to a process for converting polyketones to polyesters. More particularly, the invention involves a process whereby carbonyl (keto) groups in the polymer chain are oxidatively converted to oxycarbonyl (ester) moieties.
2. Background of the Invention
Polyketones, i.e., polymers having carbonyl groups incorporated in the polymer chain, are known and are most commonly produced by polymerizing carbon monoxide with one or more .alpha.-olefins. Polyketones of this type derived from ethylene and carbon monoxide were disclosed by Brubaker in U.S. Pat. No. 2,495,286. Numerous other liquid and gas phase procedures utilizing Ziegler and radical catalysts have been described in the prior art for polymerizing carbon monoxide with ethylene and other olefinically unsaturated monomers. A general review of the properties, preparations, reactions and uses of olefin-carbon monoxide copolymers can be found in the Encyclopedia of Polymer Science and Technology, Vol. 9, p. 397-402, John Wiley & Sons, Inc. (1968).
Carbon monoxide is also known to be copolymerizable with a variety of functionalized vinyl monomers to produce polyketones having pendant functional groups. For example, copolymers of carbon monoxide with vinyl halides, most commonly vinyl chloride, are reported by Wescott et al in Macromolecules 17, 2501 (1984), Kawai et al in J. Polym. Sci., A-1 10, 1709 (1972) Weintraub et al in Chem. Ind. 1976 (1965) and in U.S. Pat. No. 3,790,460. The copolymerization of carbon monoxide with styrene and vinyl chloride is disclosed by Kawai et al in J. Polym. Sci., Polym. Chem. Ed. 12, 1041 (1974). Methyl methacrylate, acrylonitrile, vinyl chloride, vinylidene chloride and styrene have also been copolymerized with carbon monoxide using azobisisobutyronitrile catalyst by Otsuka et al in Die Makromolekulare Chemie 103, 291 (1967). Terpolymers of carbon monoxide, ethylene and vinyl acetate are similarly disclosed in U.S. Pat. Nos. 4,172,939, 4,137,382 and 3,780,140. Additionally in U.S. Pat. No. 3,780,140, the terpolymerization of ethylene and carbon monoxide with methyl methacrylate, vinyl propionate, methyl vinyl ether and isobutyl acrylate is disclosed. European Patent Application EP No. 281139A2 discloses terpolymers of ethylene, carbon monoxide and maleic anhydride.
Various procedures are known for the chemical modification of polyketones. U.S. Pat. No. 2,457,271 discloses a method for modifying monoolefin-carbon monoxide copolymers to increase the degree of unsaturation by heating the copolymer in a solution of an organic solvent with a minor amount of an alkali metal hydroxide. The copolymer is reacted until the oxygen content is decreased by at least 5% or the iodine number increased to at least 25. Modification of polyketones (monoolefin-carbon monoxide copolymers) by reaction with hydrazine hydrate and related nitrogen-containing compounds is described in U.S. Pat. No. 2,457,279. A process for reacting polyketones with hydrogen cyanide to prepare polycyanohydrin resins is disclosed in U.S. Pat. No. 2,495,284.
U.S. Pat. No. 2,495,292 discloses the catalytic hydrogenation of monoolefin-carbon monoxide polymers in the presence of a nickel catalyst to reduce the carbonyl groups to secondary alcohol groups and obtain high molecular weight polyhydric alcohols. U.S. Pat. No. 2,846,406 relates to a process for reacting monoolefin-carbon monoxide copolymers with formaldehyde and specific ammonium or amine salts to produce polyamines of relatively high molecular weight. Another process for modifying monoolefin-carbon monoxide copolymers by reaction with hydrazoic acid in the presence of an acid catalyst is disclosed in U.S. Pat. No. 3,068,201.
Processes for producing thermoplastic polymers from polyketones are also disclosed in U.S. Pat. Nos. 3,979,373 and 3,979,374. The products of U.S. Pat. No. 3,979,373 are polymeric furan derivatives obtained by reacting an equimolar alternate copolymer of ethylene and carbon monoxide with a strong acid, e.g. sulfuric, phosphoric, p-toluene sulfonic, etc., at 40.degree.-200.degree. C. The polymeric pyrrollic polymers of U.S. Pat. No. 3,979,374 are obtained by reacting an equimolar alternate copolymer of ethylene and carbon monoxide with a primary monoamine in the presence of strong acid and a solvent at a temperature from 40.degree.-100.degree. C.
U.S. Pat. Nos. 4,616,072 and 4,687,805 disclose halogenating ethylene-carbon monoxide copolymers by contacting said copolymers in a liquid medium and in the presence of an anionic halogenation catalyst selected from Lewis acids and Lewis bases.
The oxidation and chain cleavage of ethylene-carbon monoxide copolymers to produce mixtures of .alpha.,.omega.-dicarboxylic acids ranging from succinic acid through dodecanedioic acid and possibly higher and their corresponding esters is disclosed in U.S. Pat. No. 2,436,269. The oxidation is typically accomplished utilizing nitric acid and a vanadium oxidation catalyst, e.g. vanadium pentoxide or ammonium vanadate. Other oxidizing agents which are disclosed include the higher oxides of nitrogen, chromic acid, permanganates, molecular oxygen or air, or mixtures of these.
It would be highly advantageous if a process were available whereby carbonyl groups incorporated in a polymer chain, such as in the above-described polyketones, could be readily oxidized to ester groups. It would be even more advantageous if this conversion could be accomplished without significant cleavage of the polymer chain, i.e., without substantially altering the molecular weight and molecular weight distribution of the polymer, and without affecting other functionality present in the polymer. It would be still more advantageous if the degree of oxidation could be easily controlled so that substantially all or only a portion of the carbonyl groups could be converted to oxycarbonyl moieties. These and other advantages are realized by the process of the present invention and will be described in more detail to follow.